Utilization of leather waste



Patented Mar. 15,1949

UTILIZATION OF LEATHER WASTE Morton Abrahams, Yonkers, N. Y.

N Drawing. Application November 24, 1945,

Serial No. 630,701

1 Claim. (Cl. 260-8) The present invention relates to a process for utilization of leather scrap. More particularly it relates to a process for preparing from chrome leather scrap a plastic material that can be rolled, milled or otherwise processed into sheets or other forms.

It is an object of the invention to provide a material that can be used for floor coverings, gaskets and insulating materials.

It is a further object to provide'a material suitable as a substitute for leather and as a coating on cloth and other backing material.

Many other uses will also suggest themselves to a man skilled in the art.

Briefly described, the invention includes a preliminary detanning and reducing step in which the leather scrap is partially freed of tanning compounds, such as chromium salts in the case of chrome leather, and reconstituted into a plastic mass by chemical means. On removal of the chromium salts, the leather scrap is converted, to a large extent, to a gelatinous condition due to the at least partial reconstitution of the collagen and other gelatinous elements in the hide. After washing and pressing to remove excess water, the mass is thoroughly mixed with a suitable resin to which a plasticizer is added in a mechanical mixer. Fillers or dyes or both may be added in this mixing operation. The mass is then dried, rolled, or otherwise milled into sheets or shaped suitable for the desired use.

The detanning and reducing step is preferably carried out in a wooden vat at about room temperature. The chrome tanned scrap is placed in the vat and covered with a dilute solution of a mineral acid such as phosphoric or sulphuric acid at a concentration of about 2% to 3%. The mass is stirred to ensure complete exposure to the action of the acid and is allowed to remain in the vat until it is soft and plastic. This will take place in a longer or shorter time in accordance with fineness of division of the scrap, but in any case should be complete in about 24 to 48 hours.

On removal of the mass thus produced, it is found to be quite gelatinous and plastic, the collagen of the leather being now to a large extent free from the chromic salts with which it had been reacted in the tanning process. There remains, however, a greater or less amount of stringy material consisting of fiber not completely freed from tanning agent. It is next washed with water until it is freed from acid and is then pressed to remove excesswater, the mass after pressing still, however, retaining a moisture content of about 70% or less.

The doughy, plastic mass is then transferred to a mixer, such as a Banbury mixer. Asolutlon of a resin, preferably a vinyl resin in acetone and a plasticizer such as dibutyl phthalate or that known commercially as Flexol 3 GH are added to the mass and thoroughly mixed therewith. On the other hand, the vinyl resin and plasticizer may be added as a water emulsion or dispersion with excellent results.

Among the vinyl resins that can be used are polyvinyl acetates of various molecular weights and melting pointspolyvinyl acetate-butyrate, polyvinyl chloride and the copolymers of vinyl acetate and vinyl chloride. Other thermoplastic materials suitably plasticized can, however, be used, such as acrylic esters or the cellulose esters. The mixing operation requires about a half hour but must be continued until a sample taken out and lightly pressed shows a coherent mass and does not separate but becomes stringy and not tacky when rolled in the hand.

The batch is then taken from the mixer and dried at a low temperature of about F. in a drying alley with fans drawing out the moisture from time to time until it is dried to a very small water content, 8% or less. It is then milled at a temperature of about F. and drawn from the heater rolls in flexible sheets. These sheets after rolling are resilient and do not deteriorate with age. They can be further pressed under high pressure at temperatures to suit the quality of the finished material for the desired use.

I give the following specific example as illustrative 1f the process:

- Pounds Dry chrome leather scrap 100 Water 600 85% phosphoric acid 18 Pounds Methyl acetone 50 Polyvinyl acetate resin 50 The acetate is thoroughly dissolved in the acetone with 10 lbs. of plasticizer, such as dibutyl phathalate, prior to addition to the mixer. Or theresin solution and the plasticizer may be added as a water emulsion or dispersion. Fillers such as ground cork, wood pulp, and the like, may be 1 the mass in the Banbury mixer. The whole is thoroughly mixed in the mixer and then removed and thoroughly dried and rolled into sheets. It may then be moulded or formed into desired shapes under heat and pressure.

The. proportions given in the abqve specific example may be varied in accordancenwith the use to which the final material is to be applied. There may be, for instance, more or less plasticizer or more or less or the thermoplastic resin required to meet the desired purpose.

Leather is the result of the reaction of a tanning agent with gelatinous and albuminoid matter in the hide. These reactions produce a series of insoluble compounds and render the hide firm, durable and to a considerable degree impervious to water. 'My detanning process restores partially but not completely the original condition of the is incomplete. The amount of such material can be controlled and'it may be said as a general proposition that a certain amount of such incompletely reacted fibers is beneficial in that it serves as a binder and that, further,- the amount ofsuch material may be varied in accordance with the purpose for which the materialis to be used.

Having thus described my invention, what I claim is:

. 4 The process of producing. a leather substitute material that comprises mixing in a vat 100 parts I by weight of chrome leather scrap with 18 parts by weight of phosphoric acid dissolved in 600 parts 5 by weight of water, and thoroughly stirring the same until said scrap is reduced to a generally gelatinous mass containing leather fibers only partially reacted with said phosphoric acid; washing said mass to remove said acid and salts formed thereby; then mixing said mass with a solution of 50 partsby weight of vinyl acetate in 50 parts by weight of acetone and 10 parts by weight of dibutyl phthalate in a mechanical mixer; removing the resulting product from said mixer and drying and processing the same to the desired shape.

MORTON ABRAHAMS.

REFERENCES CITED 7 The following references are of record in the '20 file of this patent:

.UNITED STATES PATENTS Number Name Date 2,148,904 Horowitz Feb. 28, 1939 5 2,184,467 Pierson Dec. 26, 1939 2,243,700v Gutterman May 2'7, 1941 2,286,038 Pierson June 9, 1942 2,370,457 Gocher Feb. 27, 1945 3o FOREIGN PATENTS Number Country Date 903,303 Germany Mar. 6, 1941 OTHER REFERENCES Lollar: Journal Amer. Leather Chemists Assoa,

vol. 34, 1939, DD. 556, 557-, 564, 565. Craemer: Kunststofie, vol. 30, No. 11, 1940, pp. 357 and. 341.'

Du Pont Technical Bulletin No.- 4-243, Poly- 40 vinyl Acetate. 

